1. Field of the Invention
The present invention relates to a recording medium type determining apparatus and a recording medium type determining method for determining the type of a recording medium based on a radial push-pull signal.
2. Description of the Related Art
There have been known recording media based on various standards including optical discs such as a DVD-ROM (Digital Versatile Disc—Read Only Memory) as read only recording media with information previously recorded therein and used only for reproducing the information therefrom, and those such as a DVD-R (Digital Versatile Disc—Recordable) and a DVD-RW (Digital Versatile Disc—ReWritable) as writable recording media in which information can be recorded. In the DVD-ROM, a bit array is formed in a spiral form on the base plate, and information is reproduced by irradiating a light beam onto this bit array. On the other hand, in the DVD-R or DVD-RW (sometimes described as DVD-R/RW hereinafter), a guide groove called as wobbling groove is formed in a spiral form on the base plate, and information is recorded therein or reproduced therefrom by irradiating a light beam onto this groove.
For recording and reproducing information, focus servo control and tracking servo control for a light beam are required, but in the DVD-ROM, as the radial push-pull signal at a sufficient level can not be obtained from the read signal, different tracking servo control systems are employed for the DVD-ROM and DVD-RW respectively. More specifically, in the DVD-ROM, the tracking servo control system based on the DPD (Differential Phase Detection) method is generally employed, while in the DVD-RW, the tracking servo control based on the DPP (Differential Push-Pull) method is generally employed.
For the reason as described above, the type of a recording medium set on the information recording/reproducing apparatus needs to be determined, and as the technology for determining the type of a recording medium, there has been known, for instance, the recording medium type determining apparatus as described in Japanese Patent Laid-Open Publication No. HEI 10-302381. This determining apparatus operates based on the fact that the amplitude of a radial push-pull signal obtained when a light beam is moved in the radial direction of a disc in the DVD-ROM is different from that in DVD-R. This determining apparatus is based on the configuration in which, during reproduction with the tracking servo control for a light beam kept open, the level of a radial push-pull signal is compared to a reference level, and the type of an optical disc is determined according to the result of the comparison (Refer to page 4, line 35 to line 50 in the left column of the Publication).
However, in some DVD-ROMs, the amplitude of the radial push-pull signal is relatively large, and with the determining apparatus described above, sometimes it is difficult to set a reference level, and erroneous determination of a disc type may be performed.